The objective of this research project is to design, develop, and evaluate a trileaflet valve fabricated from polyolefin rubber. This valve would be useful in blood pumps being developed for cardiac assist and replacement, as well as for clinical cardiac valve replacement. A polyolefin rubber, Hexsyn, has been developed specifically for a long flex life and has already demonstrated excellent stability and endurance in flexure, is nontoxic, and is currently being used as a blood pump diaphragm. This material can be compression molded into virtually any shape. Good blood compatibility of this material is achieved by biolization of the surface by coating with insoluble, crosslinked protein coatings. Since anticoagulants are not required with the biolized materials, the successful completion of this project offers a valve with all of the advantages of natural tissue valves combined with long-term durability inherent in the rubber. This research project involves the formulation and use of a rational design procedure to optimize the function and endurance of the valve. The valve will be fabricated, evaluated for performance and endurance in vitro, and evaluated for long-term blood compatibility and function in vivo. The success of this project will benefit patients requiring cardiac valve replacement or permanent type blood pumps.